Method and apparatus for winding coils



Jan. 6, 1942. c. P. 'BQUCHER A 2,259,405 METHOD AND APPARATUS FOR WINDING COILS Filed Aug. 1e, lss'' I Patented Jan. 6, 1 942 APPARATUS Foa WINDING coILs Charles Philippe Boucher, Jersey City, N. J., assignor to Boucher Inventions, Limited, a. corporation of Delaware Application August 16, 1937, serial No. 4159,401

ME'ruon AND 13 claims. (ci. 242-10) Myinvention relates to high voltage and/or high frequency electrical apparatus and more particularly to' induction coils employed in such apparatus, and'to an art of producing the same.

As conducive to a clearer understanding of certain features of )my invention, itmay be noted at this point that .in low-voltage electrical apparatus. say 1000 volts or under, and at commercial frequencies, say 60 cycles, the induction coils employed in such apparatus can be so deslgned 55 mechanically by ordinary manufacture that the coil dimensions are not excessive, and these coils give good results.

In high power electrical apparatusv where A One of the objects of my invention is the pro- 5 heav'y currents are encountered and the coils duction in a simple, direct and economical manare formed of heavy gauge Wire, 'such as No.v 10 ner rof high voltage and/or high frequency inwire or larger, it is the usual practice to subduction coils 'which are particularly adapted to merge the coils in oil. This effectively eliminates withstandlthe many varying conditions enccunexcessive heating. In addition, the freely flowing tered infactual practical use. l0 oil prevents the formation of gas and air pockets Another. object is the provision of an inducaround the coils. High frequency discharges are tion coil which is compact, strong and rugged, 'substantially eliminated in such apparatus. Any which inherently possesses a minimuml leakage coil discharges are of such short duration that reactance, which provides excellent elimination they represent no source of danger. Thus, in of heat under operating conditions, and which is l5 electrical apparatus employing coils operated in peculiarly free from bursting .or leaking under oil, satisfactory performance at high voltage is the severe conditions encountered in high voltreadily obtained. vSuch apparatus, however, is

' age and high frequency apparatus. exceedingly bulky and expensive. v

Still another object of my invention is the pro- In the rapidly developing modern fields of elecvision ofapparatus for manufacture of coils of 2n trical activity, where-electrical apparatus of only the type described, which is rugged in construcmoderate current ratings are employed, such tion and which is simple, efficient and economfor example as voltage regulators, high voltage ical in operation. luminous tube supply (the conventional neon Other -objects in part will be obvious and in tube), the high voltage supply ,for X-ray mapart pointed out hereinafter. K 2f\ chines, automobile ignition coils, and the like,

The invention accordingly consists in the c'oxnthe high voltage current employed often is4 also bination of elements, features of construction of high frequency. say upwards' of many thouand arrangement ofV parts and in the several l sands of cycles per second. The nature of the stepsf'and the relation of each of the same to equipment issuch as not to warrant oil as an one orno're'of the `others as-described herein, 39 insulating medium. Here disturbing factors, the scope of the application of'which is set forth such as, local generation 'of heat, local capacin the following claims. a itance, electrical leakage, particularly 'at the In the accompanying drawing illustrating cersides or margins of the'coils, chemical effects, tain features of my invention: high frequency discharges, and the like,'all or a Figure 1 represents a side elevation view of my part of which are 'encountered in present'day apparatus, certain portions being shown in secpractice, must be minimized to the point of being tion to more clearly disclose certain features of negligible, in order to ensure long and satisfacthe invention. i tory operation of the coil. Experience has shown Figure 2 is a cross sectional view of the 'appa- -thatit is these factors, substantially in theorder ratus shown in Figure 1 as seen along the line 40- named, which result in premature failure of coils 2-2 of that figure, operated at high voltages and/or high frequen- Figures 3 and 4 illustrate certain modified cies. forms of my coil-winding apparatus-as seen in According to accepted practice, induction coils vertical section, and are wound dry, as by means of `a machine. When Figure 5 represents a detached view, on an 4" completed, the coils comprise a hollow core, conenlarged scale, of a coil-winding form as used Aveniently of paper or otherfiibrous material, on in the apparatus of any one of Figures 1, 3 and 4. which are superposed successive and alternate Like reference characters denote like parts layers of fine wire and paper. y throughout the several views of the drawing. m Thereafter, following one conventional method, the coils are first heatedv and then placed in a vacuum tank carrying an appreciable vacuum head. whereupon a hot, molten insulatinglcompound is introduced, filling the coils by capillarity. Thereupon positive pressure is applied, all 4voids of the coil then supposedly being filled with the compound. The coils are withdrawn and allowed to cool. As a practical matter, when this method is employed, it is impossible, regardless of the degree of vacuum, amount of pressure, or vtype of insulating compound used, to rid the coils completelyof moisture, and free spaces unfilled with compound, are left in the coils.

In a second conventional method ther coils, after being air-heated to dryness, are placed on 4forms which tightly grip the coils about their entire periphery. After the coils, thus gripped, are placed horizontally, molten insulating `compound is poured on the upper parts ofthe coils coils are then heated to harden the compound,

whereupon, after cooling, they are ready for use. in thiscase, the entire center of the coil retains gases and moisture, and the coil' is subject to unexpected failure under high voltage and/or high frequency conditions.

The prior art coils when subjected to high voltage and/or high frequency service fail because local high voltage discharge occurs where.. ever air spaces are found within the coil. The discharge usually begins with aso-called corona or brush discharge. Heating results, which may be accompanied by charring of insulation and the short-circuiting of adjacent turns or successive layers of the coil. Since the breakdown phenomenon is aggravated as the discharge space becomes larger, the coil soon goes out of operation. Furthermore the layers of coil winding serve as condensers, and taken in conjunction with the inductance of the coil, may set up an oscillating condition giving rise to voltages which will break down an air pocket giving sparking between layers. Since air pockets initially contain oxygen, the high voltage discharge converts the oxygen into ozone, which, under the action of the local heat generated by the discharge, ex'

pands and forces its way out of the coil, thus destroying the insulation at the surface of the cnil. In addition, chemical attack of the conducting wire is frequently encountered, due to the powerful oxidizing action of the ozone.

Dinculty is also occasioned, when ordinary methods of winding in air and subsequent impregnation are used with temperatures but.little above the boiling point of water. say about 220, due to the fact that al1 moisture remaining in the coils in the form of water vapor, not being driven off inasmuch as a perfect vacuum cannot type, which are filled with compound having 'ttle elasticity, either the coils yield under the stress thus applied or else the 'movement of the coils fractures the compound, producing the detrimental phenomenon known as breathing, that is, the admission of outside air into the compound through the cracks which are formed.

Again, it is common practice, in coils used for neon, X-ray, or other high frequency transformers, `to provide what is known as a sparking margin, that is, a space of from one sixteenth to one-quarter of an inch between the edge of the paper or other insulation, and the rst and last turns of the layer of wire placed adjacent thereto. This spacing serves to prevent leakage and sparking and provides in coils intended to operate at say 2000 volts or more, one of the best factors of safety for the coil. Now, when a coil is machinewound, it is practically impossible to ensure that the corresponding edges of the layers of insulation are flush. Where unevenness is had pockets are formed. In addition, these Aedges frequently contact each other, forming closed pockets which are not penetrated by the compound during the subsequent treatment. Where pockets are formed gases and moisture are trapped therein. In subsequent useelectrioal leaks become frequent, and after a time the coils tend to fail due to heat and chemical action on the conductors.

An object of my invention, therefore, is to eliminate the above-mentioned difficulties found in coils of the prior art, and to produce a coil which is compact and closely wound, which is free from air-pockets, gas and moisture both between layers of windings and between coil edges or margins, and which is of lowleakage reactance and high heat-dissipating efficiency. Another object is to providev a simple, practical and efficient method and apparatus for economically producing such a coil.

Referring now more particularly to. the practice of my invention, attention is directed to Figures 1 and 2. A container I, preferably formed of metal, is provided of any desired shape, shown as cylindrical, with rounded, substantially semi-spherical Abottom 2. The container l is adapted to be filled to a convenient level 3 with a suitable 'insulating and impregnating material, indicated generally by the reference numeral 4, such for example as rosin, parailin, wax, insulating varnish, or the like. The compound preferably is of such character as to be either plastic or solid at room temperature with a melting or fusing point somewhat above the boiling point of water. The melting-point, of course, is below that at which paper will char. A convenient melting-point range for the usual conditions of practice is roughly, 230-350 F. The surface of the compound preferably is maintained freely open to the atmosphere. All moisture present in the compound ,thus will be vaporized andeliminated from the system, since the temperature is sufllcient `to vaporize moisture even at the pressure existing at the lower part of the container.

To maintain the compound in the container at a desired temperature, suitable conventional heating means are provided. While these heating means are shown in Fig. las comprising electric elements 5 5, it is at once evident that where desired, the Aheating can be accomplished by steam` or hot gas jackets and the like.

. A winding machine isv employed in connection with the container l, certain portions of this masource, not shown, across conventional guide means, such for example as the schematically illustrated guide sheave Il and bracket i2, to the winding form 1. The temperature of the impregnating compound 4, the linear rate of feeding the wire I0, and th'e location of form 1 below the level of the compound all are so selectedand correlated that between the timethat the wire I@ Venters the compound 4 and the time that it reaches the form 1, it will be substantially en-` tirely freed of all traces of moisture, the moisture, quickly vaporized, passing freely upwardly to the surface 3 of the compound, where it escapes, even when the temperature of the compound 4 is but little in excess of the boiling point of water. For plain enamel-covered wire, good results are had where the form is located, for example, at least one inch, and preferably several downwardly moving strip. To achieve this reinches, beneath the surface of the compound, it

beingunderstood that the depth to which the wire extends is appreciably in excess of this gure.

The wire I0, which usually is of'small gauge, say No. 26 or under, is wound roundform 1 until a complete layer is. built up. At this time a layer of flexible sheet insulation, such as paper or the like, is introduced to serve the combined purpose of a spacer and an insulator-between adjacent layers of conducting wire.

For reasons pointed out hereinbefore, it is essential that all moisture and entrapped gases be removedfrom this insulation before it is wound on the form, particularly to prevent local con denserl action, and mechanical expansion of gases and water vapor, as well as chemical action of the gases. Now, considerable practical diiiiculty is encountered in removing bubbles of gases entra-pped on the insulation because of the fibrous nature of th'e latter, presenting a` large number of minute interstices and crevices from which it is difiicult to dislodge adsorbed vapors and gases.

To accomplish the desired end, sheet insulation I3, supplied from a suitable source, such as roll I4, ispassed upwardly in the direction of the arrow and over'suitable guide means I 5 and then downwardly into thecompound present incontainer i. The hot compound vapori'zes any moisture present lin or on the insulation. In its travel the insulation is conducted downwardly through compound -4 to such'depth` that the hydrostatic pressure of the compound overcomes the surface' tension offanv bubbles of gas which may be' entrapped within the insulation or adsorbed on its surface.l Ordinarily a depth of 30 inches is' sufiicient. For .some typesof insulation, however.

and especially with lowwinding speeds and good'j To facili-l sultylower guide roller I6 is positioned almost immediately beneath 'guide I5.

Contact between strip I3 and the walls of container I, and possibleundue heating of insulation and consequent charring, is preventedby guide I8 mounted onv the cooler upper-part of the container. Guide I l and roller I8 maintain strip I3 an even, safe distance from the rear wall of container I.

After the insulation has passed down through the compound 4, it is directed by guide I6 upwardly and around a third guide, such as roller I1. From the roller I1, the strip I3 passes directly to the winding form 1. It is to be noted that the strip `is maintained beneath the surface of the compound prior to the winding operation, as weil as during that' operation. A suitable knife or cutting means, not shown, is provided to cut the insulation after a desired amount'has been wound onto the form. Other means, not shown, are provided for starting the 'insulation after the next layer of wire has been wound onto the form.

To ensure that the gases which are liberated from the paper will. escape to the 'atmosphere without coming into the region ,of the form 1, I

provide a partition, or bafile I9 of any conven-v termed, a mainy chamber 20 across the roller I1,

but below the surface 3, tol form 1. As suggested inthe foregoing, the partition I9 separatesthe container I into what is known as a main chamber 20 and a smaller, degasifying and dehydrat- `ing chamber 2|. To the end of ensuring the desired isolating action, that is, the prevention oi' escape of liberated gasesto the form, the partition I9, as illustrated in Fig. 2, is made some- V what wider than the strip I3.

In winding a coil many turns of wire must be wound before a layer of wire is compieted.,. Following this a. single turn of paper I3 is required. Accordingly the paper I3 remains in the degasifying and dehydrating chamber, between the moment at whichitis introduced into the `compound and the timewhen it reaches the vlovvermost point in its travel, al time sufiicient ,for thev removal of all entrapped gases and" all moisture.

It is essential'that at no time after the strip i3 andthe wire I0 have been introducedinto the compound 4, -until theylrhave been wound on form 1, will they be exposed to the atmosphere'. Rollei I1, baille I9, andform 1 are-relativelypositioned to achieve this result.

'. Whilein the above, `consideration is given to the Winding of a single coil, it will be understood that my invention is adaptable to the winding of a plurality'of coils simultaneously.l In thisembodiment, and having particular reference to Fig.

s, it is to be' noted that an'increase is made in' the dimensions of the container I in 'order toactate the free passage of the liberated gases itis c commodate the elongated form -22. Insulation 4stripfIS is offincreased width as indicated. `A'

plurality of wires or conductors I0 are lead' into the container and wound onto the elongated corel tube mounted on the winding form. In lthisway a plurality of coils 9 are built up'on the form 22,

with open spaces 23riilled only lwith insulating .Y

' bodiment, as well as in those of the remaining figures, I have axed the winding form or its spider, as the case may be, to the arbor by keying,

order to ensure uniform heating of container 29, and hence of the compound 4, and to eliminate local hot spots with consequent partial decomposition of compound, insulationi3, or the insulation on the wire III, I distribute uniformly about the chamber 34 a plurality of electrical heating elements 35. These preferably are of substantially the same electrical rating. It is to be understood, however, that I am by no means comalthough, of course, any other desirable means of I securing the two elements together may ,be employed.

Y It is to be noted that since the strip I3 becomes thoroughly impregnatedwith the compound 4 before it is wound on the coil, and further since there are no gases in the compound or on the strip by the time the latter reaches the form 1, the ends or margins of the coils may be sealed or collapsed without the formation of gas pockets as ordinarily encountered in the prior art. A further `feature ofmy invention, therefore, is the provision of means for clamping the ends of the winding form, thereby substantially c sealing the marginal ends o'f the layers of the strip or insulation I3 built up thereon andpreventing the leakage or drainage out of the ends of the coils of the compound 4, during the ref moval lof the form from the container I. The wound coil is then removed from the form after the compound has cooled and hardened.- Although such clamping means may take any one of a plurality of different embodiments, and is applicable to the production of one coil, as well as a plurality, I have elected to show one such embodiment 'in Fig. 5. Arbor 24, vshown as threaded at 25-25 adjacent to vbut just short of each end, is adapted to receive threaded clamping collars 2B, 21. Thesey are loose while in the compound 4, but .-are tightened, as by a wrench or the like, before the form is withdrawn from After removal of form 22 from container I',

the core tube with its plurality of coils thereon is vremoved -from the form. After the impregnating compound has solidified on the coils, then thetube is sawed, as along lines 2828, to separate ther several coils. The spaces 23 are of sufficient width to provide sparking margins of satisfactory length at the edges of the completed coils.

Certain desirable results are achieved in coil production employing a modied form of coritainer, as indicated in Figure 3. A container 29 is provided, iilled with the compound 4 to the level 3. In the container 29 is housed a rotatable arbor 39, on which is mounted, as by keying, a winding form 3I, similar to the form 1A of Fig. l. On this form there is mounted a core mitted to the yuse of electrical heating means to the exclusion of all others, and when I nd it desirable to so do, I contemplate the use of the chamber 34 as a chest for steamv or hot gases, with suitable modication in such case for the provision of inlet and outlet.

In fthe embodiment illustrated in Figure 3, the partition 33, dividing the interior of the container into a degasifying and dehydrating chamber 31 and a main chamber 39, extends to or adjacent the bottom of the container 29, and stops short of the surface of ythe compound. The arrangement oi the rollers I3 andv I1 is such that the strip I3 passes both downwardly and upwardly through the degasifying and dehydrating chamber.l Any given element of the strip I3 remains in the chamber 31 during the entire time that -a layer of wire I0 (constituting a large number of turns of wire) is being wound on the coil, hence, there is ample time for the removal of all moisture and gas during the down and up travel of the strip I3 lthrough the chamber. Since the strip travels substantially vertically through chamber 31, it oiers substantially no impedance to the ilow of liberated gases up through the chamber.

A'further modified form of my apparatus is iny dicated in Figure 4. In this modification the container 39, as distinguished from the containers I and 29 of Figures 1 and 3, respectively, is of Just sufficient size to house the winding form assembly comfortably but comparatively snugly, with sufficient room to receive an adequate supply of compound 4 up to level 3. This container pro- V vides what I choose to describe as a main chamber 40. A well 4I, the walls of which are of metal or insulating material, depending upon choice, providesan elongated degasii'ying and dehydrating space 42, vof length sumcient to ensure that the hydrostatic pressure of the head of the compound is sufficientV to overcome bubbles of gas entrapped on the fibrous insulation I3 passingthrough the compound. Well 4I conveniently is disposed laterally of the container 39 and opens into 39k at a .Junction point 43 well below the surface of the compound. Thus the compound will flow over from the container 39, filling the well 4I to 'the same level as that maintained in container 39. To ensure that sases liberated in the well 4I and escaping to the surface do not migrate into ythe .vicinity of the form 3i, a baille or partition 44 is built up from the junctionv 43 of the container 39 and well 4I. Batlle 44 extends to a point just short of the surface of th'e compound, thus effectively increasing the height of the degasifying and dehydrating chamber 42. It is -to be particularly noted that locations 'of roller I1, baille 44, and the winding means f heating chamber 34 provided between Y the container and the wall 34a substantially surrounding it. Wall 34a is formed of suitable metal or of insulating material, as found desirable.v In

form 3l are .such that at no time after strip I3 and wire I0 have been introduced into the compound 4will these two elementsbe exposed to the atmosphre until the coil is completely wound.

Shown as surrounding the container. 39 and well 4I is a heat insulating jacket y45, conveniently of metal or insulating material, and forming,

together with' the container 39 and' well 4I, a

l 2,269,405 continuous heat chamber 46. Where desired this chamber may bemade discontinuous, as for example by having a first heat chamber about the container 39, and a second, separate heat chamber about the well 4l. While AI contemplate the use of any suitable fluid heating medium in the chamber 46V, such as hot gases or steam, I have elected to show for this purpose a plurality of electrical heating coils 41, all conveniently of substantially the same electrical rating. These heating coils are disposed substantially uniformly in the chamber 46 about the container 39 and well 4I.

A construction such as that illustrated in Figure 4 is characterized by its economy in material and the amount of compound required, and by lthe space necessary for housing the assemblage.

Experience shows that coils wound in accordance with my invention and of equal current-carrying capacity as prior art coils, are of substantially smaller depth, which means smaller distance between layers of wire. The leakage re actance of these coils is appreciably less than those of the prior art. This construction permits more emcient operation. 4The compactness of the coil also tends to increase the rate of dissipating heat from its interior. This feature permits safer operation.

As a further point the distributed capacity of mycoils is -greater than those of th'e like ratings of the prior art. In fact, the distributed capacity may be. sufciently high as compared to the inductance as to prevent harmful oscillations and excessive potentials being reached, potentials which frequently are of such values as to rupture the insulation.

Thus it will be seen that there has been provided in this invention an art and apparatus for producing induction coils in which th'e various objects hereinbefore noted, together with many thoroughly practical advantages, are successfully achieved. It will be seen that the apparatus and method are simple, economical and eiicient and that the resultant coil is rugged and compact in` construction and well adapted to withstand the many varying conditions encountered in actual use. y

While, as illustrative of my invention, certain embodiments have been described, it will be un- 'derstood-that satisfactory coils are produced so long as the entrapped gases and.v moisture on the sheet insulation and wire are removed by a fusible compound. This result is achieved by immersing these materials in a fusible compound at a .tem-

perature above the boiling point of water at such pressure as to free them of adsorbed gases and vapors and then bringing them in moisture and gas-free condition to the winding form. The` coils are wound within the compound and are so removed that thev 'fused compound is prevented from escaping during the cooling and hardening thereof.

It will, furthermore, be understood that a1- though heating means preferably are provided forthe insulating compound, I can eliminate this heating of the impregnating compound where the same 'is liquid at the working temperature and is preliminarily hydrofuged to free it of moisture, and where the paper and wire are pretreated to remove substantially all moisture normally pres- `ent in these materials@ Likewise, it will be understood that in certain cases, vacuum conditions may be maintained in connection with the containersv of the various embodinrients.A The use of a vacuum facilitates moisture and gas removal and in addition aids impregnation of the paper and layers with the insulating compound.l

Since many possible embodiments may be made of my invention and lsince many changes may be made in the embodiments hereinbefore set forth, it will be understood that all matter described herein, or shown in the accompanying drawing, is to be interpreted as illustrative, and not in a limiting sense. i

1. In the production of uniformly impregnated coils free of entrapped gas and moisture particularly adapted for high potential and high frequency electrical apparatus, the art which comprises, submerging a winding'form in a fusible insulating and impregnating compound wholly 1 beneath the surface thereof, passing iiexible sheet insulation downwardly through the compound to a depth substantially greater than that of the form and then back up to the form to ensure that the hydrostatic pressure of the compound will remove substantially all -bubbles of entrapped gases from the insulation, winding on the said form while in its submerged position desired layers of conducting wire and insulation,v

insulating and impregnating compound, maintaining said compound at atmospheric pressure,

passing conducting wire into said compound,-v

passing flexible sheet insulation downwardly and substantially vertically into such compound to a greater depth-than said winding form in order that entrapped gases on said insulation are driven off by the hydrostatic pressure, then passing the insulation upwardly to the winding form, winding said insulation and said wire, while submerged, in layers onto said form, and maintaining the compound at such temperature as to fuse the same and drive off all moisture on said insulation.

3. In the production of uniformly impregnated coils free of entrapped gas and moisture particularly adapted-for high potential and high frequency electrical apparatusv the art which comprises, passing ilexible sheet insulation downwardly through an insulating compound into a degasication and dehydration space a sufcient depth to ensure that the hydrostatic pressure of the compound will remove all bubbles, of entrapped gases, then winding wire `and the de-y gasied and dried insulation onto a winding form maintained in submergedA position in a main space separate from said degasication and d'ehydration spaoe, said wire and insulation being maintained continuously submerged in s aid compound 4from the time of their introduction until wound on the form.

4.- In the production of uniformly impregnated coils free o'f. entrapped gas and moisture particularly adapted for `liigh potential and high fre-` quency electrical apparatus, the art which comprises, submerging a winding form in a fusible insulatingV and impregnatingv compound, passing flexible sheet insulation downwardly through the compound a sufficient depth to ensure that the hydrostatic pressure of the compound will remove all bubbles of entrapped gases from the insulation, winding on said form while in its submerged position alternate layers of conducting wire and said sheet insulation, and compressing the ends of the formed coil while removingthe coil from the compound, to prevent the compound rom draining olf before it hardens.

In the production of uniformly impregnated coils free of entrapped gas and moisture particularly adapted for lhigh potential and high frequency electrical apparatus, the art which comprises, submerging a winding form and a coil tube for a plurality of coils in a fusible insulating and impregnating compound, passing nexible sheet insulation downwardly through the compound a suilicient depth to ensure that the hydrostatic pressure of the compound will remove' all bubbles of entrapped gases from the insulation, winding on said tube while in its submerged position, in such manner as to form a plurality of separate coils alternate layers of conducting wire and said flexible sheet insulation, and compressing the ends of the tube with covering members while removing the same from the compound, to prevent the compound from draining off before it hardens.

6. In apparatus of the character described, coil winding apparatus comprising, in combination, a container adapted to be filled with fusible insulating and irnpregnating compound and including a degasification and dehydrating chamber, a source for supplying flexible sheet insulation, a winding form rotatably mounted in said main chamber below the normal lever of the compound therein, means for passing the insulationfrom said source to said form downwardly into thel degasication anddehydration chamber a sufficient distance under the surface of the compound to drive on gases entrapped on the insuinto a. degasifying and dehydrating chamber and a main chamber, a source for supplying flexible sheet insulation, a winding form rotatably mounted in said main chamber below the normal level of the compound therein, means for passing the insulation from said source to said form downwardly into the degasifying and dehydrating chamber a suilicient depth under the surface of thecompound to drive off gasesentrapped on the insulation and thence whilel still submerged into the main chamber to said form, and means for passing conducting wire into said compound f to the form-,so that alternate layers of insulation lation, and means for passing conducting wire into said compound to the form, so that alternate layers of insulation and wire may be built up on said form underneath the surface of said compound.

'7. In apparatus of the character described, coil winding apparatus comprising, in combination, a

container adapted to be lled with fusible insu-- lating and irnpregnating compound, means sepi arating the interior of the container at least pargasifiyng and dehydrating chamber a suicient depth. under the-surface of the compound tc 'drive off gases entrapped on the insulation, the

` liberated gases passing freely upwardly in said degasifying chamber, means passing the insulation to the winding form, and means for passing conducting wire into said compound tothe form. so that alternate layers of insulation and wire may be built up on said form underneath the surface of said compound. 8. In apparatus of the character described, coil winding apparatus comprising, in combination, a

and wire may be built up on said form underneath the surface of said compound.

9. In apparatus of the character described, coil winding apparatus comprising, in combination, a container adapted to be filled with fusible insulating and impregnating compound, a source for supplying fiexible sheet insulation, a partition in said chamber terminating short of the bottom of the latter and separating the interior thereof into a degasifying and dehydrating chamber and a main chamber, said partition being wider` than the width of the sheetinsulation, a winding form rotatably mounted in said main chamber below the normal level of the compound therein, means for passing the insulation from said source. downwardly into the degasifying and dehydratlng chamber and thence underneath the partition and directly up to the form,and means for passing conducting wire into said compound to the form, so that alternate layers of insulation and wire may be built up on said form underneath the surface of the compound.

10. In apparatus of the character described, coil winding apparatus comprising, in combination, a container adapted -to be lled with fusible insulating and impregnating compound, a source for supplying exible sheet insulation, a partition in said chamber terminating short of the normal surface of the compound and separating the interior of the container into a degasifying and dehydrating chamber and a main chamber, a. winding form rotatably mounted ln the main chamber below the normal level of the compound therein, means for passing the insulation from said source downwardly into the degasifying and dehydrating chamber a. sufficient depth under the surface of the compound to drive olf gases entrapped on the insulation. and thence back upwardly through the degasifying and dehydrating chamber and across the top of the partition, under the surface of the compound, to the winding form, and means for passing conducting wire into said compound to theform, so that alternate layers of lnsulationg and wire may be built up on the form underneath the surface of the comcontainer adapted to be filled with fusible insulating and impregnating compound, means for uniformly heating the container, means separating the interior of the container at least nartiallv pound.I

11. In apparatus of the character described, coil winding apparatus comprising, in combination, a container adapted to be filled with fusible insulating 'and-impregnating compound, a winding formlrotatably mounted in said container below the normal level of the compound therein, an elongated well comprising a degasifying and dehydrating chamber disposed laterally of said container 'and opening at its top into said container below the normallevel of the compound, a source for supplying flexible sheet insulation, means for passing the insulation from said source downwardly into the degasifylng and dehydrating chamber a suillcient depth under the surface of the compound to drive olf gases entrapped on x lwire may be .built up on the form underneath `gasifying and dehydratingchamber and over intoA the container. under the lsurface of the ccm-I surface of said compound.

12. In apparatus of the character described, coil winding apparatus comprising, in combination, a container adapted to be iilled with fusible insulating and impregnating compound, means for heating the container, means separating the interior of the container at least partially into a degasifying and dehydrating chamber andr a main chamber, a source for supplying flexible 'sheet insulation, an elongated winding form, on which a plurality of--separate coils can be wound simultaneously, an arbor extending' through said form and beyond the ends thereof and journalled in the main chamber of said container in such manner that the form will be disposed below the normal level of the compound in the chamber, means for passing the insulation from the said source downwardly into the degasifying and dehydrating chamber a sufficient depth under the surface of the compound to'drive of! gases entrapped on the insulation and thence to the form,

the v '7 means for passing a plurality oi conducting wires into said compound to the form, so that alternate layers of insulation and wire will be built up on the form as separate coils underneath the surface of the compound, and means for clamp-` ing the ends of the form to prevent draining of the hot compound before it cools and solidifles when the form is removed from the container.

13. In the production of uniformly impregnated coils free of entrapped gas and moisture particularly adapted for high potential and high frequency electrical apparatus, the art which comprises, submerging a winding form in a fusible insulating and impregnating compound, passing conducting wire into the compound to said winding form, passing' flexible sheet insulation spaced from said wire downwardly and substantially vertically into such compound 4to a greater depth than said winding form in order that entrapped gases on said insulation 'are driven oiI by the hydrostatic pressure, then guiding said submerged insulation tothe winding form, winding said insulation and said wire, while submerged, in layers on said form, and maintaining the compound at a temperature so as to fuse the'same and' drive off all moisture on said insulation.

CHARLES PHILIPPE BOUCHER. 

